A present invention relates to a steering wheel for vehicles.
Generally, a steering wheel includes an annular grip, spokes and a pad. The spokes extend from the grip towards the center of the steering wheel. The pad is located in the center of the grip ring. A metal grip core and a metal spoke core, which are made of magnesium alloy, are embedded in the grip and the spoke, respectively. A polyurethane layer covers the grip core and the spoke core. A boss including a boss body and a boss plate is connected to the spoke core below the pad by insert molding. The steering wheel is installed on the end of a steering shaft by engaging the boss with the steering shaft: The steering wheel is fixed by fastening a nut to threads on the end of the steering shaft.
In such steering wheels, when installing the steering wheel to the steering shaft, it is necessary to fasten the nut from above the boss. Accordingly, a pad that includes an airbag can not be attached on the cores in advance. The pad must be installed on the cores after the steering wheel is attached to the steering shaft.
On the other hand, it is known to employ a yoke-type boss, which is fixed to the steering shaft from the side by a bolt. The body of the yoke type boss includes a cylindrical portion with inner splines, which engage with outer splines on the steering shaft, and a C-shaped yoke portion, which is integrally formed with the cylindrical portion. Bolt holes are formed in facing parts of the yoke portion. At least one of the bolt holes has inner threads. A neck portion corresponding to the bolt holes is formed on the outer surface of the steering shaft.
After the boss is engaged with the steering shaft, a bolt is fastened in the bolt holes. Rotation of the steering wheel with respect to the steering shaft is prevented by engaging the splines of the boss with those of the steering shaft and by tightening the yoke portion with the bolt. The shaft of the bolt engages the neck portion, and axial movement of the steering wheel is also prevented.
When the yoke-type boss is used, a steering wheel assembly is installed on the steering shaft. The assembly includes the air bag device in the pad attached on the cores. Since the steering wheel is assembled before the installation, it can be transported as an assembly including the pad, which improves efficiency.
In the steering wheel assembly, the airbag device must be provided in the middle of the cores facing the driver. However, since the yoke-type boss is located in the center of the cores, supports for attaching the airbag device can not be formed in the center of the cores. This limits the formation of the airbag supports. It is necessary to make the airbag supports strong because, when the airbag is activated, a great load acts on the airbag supports. If the airbag supports are deformed when the airbag is activated, the air bag may not open in the proper direction.
Further, in the steering wheel assembly, fastening the bolt is troublesome. A worker must adjust the position of the bolt with one hand and tighten the bolt by a tool with another hand. Also, this work is done in a relatively small space, and the work takes time.
The weight of the steering wheel can be reduced by forming the cores by die casting using a light metal like magnesium. The light metal may also be aluminum or magnesium alloy. However, magnesium resists deformation. Thus, when a large load is applied to the steering wheel, the cores resist deformation. Deformation is desirable to absorb energy.
The boss will now be further described referring to FIG. 11. The boss 51 includes a cylindrical portion 52a, a boss body 52 having yoke 52b, and a boss plate 53. The boss plate 53 is welded to the cylindrical portion 52a of the boss body 52. A step-like bend 53a is formed on the boss plate 52. An insert portion 53b is on the rim of the boss plate 53 and is located toward the lower surface of the boss plate 53. When a metal core 56 is molded on the insert portion 53b of the boss plate 53 using molds 54, 55, the metal core 56 does not project forward of the lower surface of the boss plate 53.
Molten metal that flows in a cavity for molding the metal core 56 in the molds 54, 55 is subjected to high pressure, and there is a concern that the molten metal in the cavity might leak toward the boss 51, thus producing flash. Therefore, to prevent leakage of the molten metal, surfaces 55a, 54a of the inner margins of the molds 54, 55 contact the boss plate 53. In other words, the molds 54, 55 include anti-flash surfaces 54a, 55a. 
However, since a bend 53a is formed on boss plate 53, the width W2 (as measured in the left to right direction of FIG. 11) of the anti-flash surfaces 54a, 55a is too small. Therefore, flash, which extends from the inner edges of the molds 54, 55, is not prevented completely.
An installation structure of a prior art boss will now be described with reference to FIG. 14. As shown in FIG. 14, a circular through hole 252 is formed on a boss plate 251. A lower end of the cylindrical portion 253a of the boss body 253 occupies the through hole 252. The boss plate 251 is welded to the cylindrical portion 253a of the boss body 253. The projection amount P2 of the boss body 253 rearward of the boss plate 251 (towards the airbag) is relatively large, and the boss body 253 thus interferes with the installation of an airbag device. The size of the steering wheel 11 also increases.
To solve this problem, it is possible for the boss body 253 to be further inserted forward in the through hole 252 of the boss plate 251 and then fixed by welding. In this way, the rearward projection amount of the boss body 253 from the boss plate 251 is reduced, and the size of the steering wheel is reduced. However, when the boss body 253 is further inserted in the through hole 252 of the boss plate 251, a slit 253c of a yoke portion 253b overlaps the weld bead 254. The part of boss body 253 with slit 253c is not uniformly deformed during welding, and strain is caused from welding. The length of the slit 253c may be shortened. However, if this were done, the axial length of the yoke portion would be shortened, and consequently the yoke portion 253b will not easily flex. Therefore, when a bolt is tightened in the bolt hole, the radius of the yoke portion 253b cannot be easily reduced. As a result, the steering wheel 11 may not be secured to the steering shaft 30.
A first objective of the present invention is to provide a steering wheel that has a strengthened airbag supports on the cores.
A second objective of the present invention is to provide a steering wheel formed by die casting and that absorbs energy when a predetermined load is applied.
A third objective of the present invention is to provide a steering wheel that makes the work of installing the steering wheel to the steering shaft faster and easier.
To achieve the above objectives, the present invention provides a steering connected to a distal end of a steering shaft with a boss, the steering wheel having a grip for rotating the steering shaft, the steering wheel comprising: a metal grip core embedded in the grip; a plurality of spokes that extend from the grip; a metal spoke core embedded in each spoke, wherein the spoke core is integrally molded with the grip core by die casting; a layer of material covering the grip core and the spoke core; a pad, which is located over the boss in the center of the grip; a cylindrical portion, which is part of the boss, wherein the cylindrical portion receives the distal end of the steering shaft, wherein the cylindrical portion is a part of the boss; a fastening mechanism for fastening the boss to the steering shaft, wherein the fastening mechanism is integrally formed with the cylindrical portion; a boss plate fixed to the cylindrical portion of the boss, wherein the boss plate includes a rim which is embedded in the spoke core, wherein the boss plate includes a deformable portion, which is deformed when a predetermined load is applied to the grip.
The present invention further provides a steering wheel connected to a distal end of a steering shaft with a boss, the steering wheel having a grip for rotating the steering shaft, the steering shaft comprising: a grip core embedded in the grip; a plurality of spokes extending from the grip core; a spoke core embedded in each spoke, the spoke cores being integrally molded with the grip core by die cast molding; an airbag device located behind the boss; and a pair of ribs formed on the spoke core, the cross section of the spoke core being U-shaped, wherein an airbag support for attaching the airbag device is integrally formed on at least one of the ribs.
The present invention provides a steering wheel connected to a distal end of a steering shaft with a boss, the steering wheel having a grip for rotating the steering shaft, the steering wheel comprising: a metal grip core embedded in the grip; a plurality of spokes that extend from the grip; a metal spoke core embedded in each spoke, wherein the spoke core is integrally molded to the grip core by die casting; a cylindrical portion, which is part of the boss, wherein the cylindrical portion receives the distal end of the steering shaft; a yoke integrally formed on the cylindrical portion, wherein the yoke has a pair of arms for fastening the boss to the steering shaft; a bolt hole provided in each arm of the yoke, a bolt occupying the bolt holes for fastening the arms of the yoke and fixing the steering wheel to the steering shaft; a neck formed in the steering shaft, wherein the bolt engages the neck; and a bolt retainer for holding the bolt, the bolt retainer being axially aligned with the bolt hole, wherein the bolt retainer temporarily retains the bolt in an initial position, wherein the distal end of the bolt is spaced from the neck portion and is located in the entrance of one of the bolt holes prior to installation of the steering wheel.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.